<s>
In	O
computing	O
,	O
PSE-36	B-General_Concept
(	O
36-bit	O
Page	B-General_Concept
Size	I-General_Concept
Extension	I-General_Concept
)	O
refers	O
to	O
a	O
feature	O
of	O
x86	B-Operating_System
processors	O
that	O
extends	O
the	O
physical	O
memory	O
addressing	O
capabilities	O
from	O
32	O
bits	O
to	O
36	O
bits	O
,	O
allowing	O
addressing	O
to	O
up	O
to	O
64GB	O
of	O
memory	O
.	O
</s>
<s>
Compared	O
to	O
the	O
Physical	B-General_Concept
Address	I-General_Concept
Extension	I-General_Concept
(	O
PAE	O
)	O
method	O
,	O
PSE-36	B-General_Concept
is	O
a	O
simpler	O
alternative	O
to	O
addressing	O
more	O
than	O
4GB	O
of	O
memory	O
.	O
</s>
<s>
It	O
uses	O
the	O
Page	B-General_Concept
Size	I-General_Concept
Extension	I-General_Concept
(	O
PSE	O
)	O
mode	O
and	O
a	O
modified	O
page	O
directory	O
table	O
to	O
map	O
4MB	O
pages	O
into	O
a	O
64GB	O
physical	O
address	O
space	O
.	O
</s>
<s>
PSE-36	B-General_Concept
'	O
s	O
downside	O
is	O
that	O
,	O
unlike	O
PAE	O
,	O
it	O
does	O
n't	O
have	O
4-KB	O
page	O
granularity	O
above	O
the	O
4GB	O
mark	O
.	O
</s>
<s>
PSE-36	B-General_Concept
was	O
introduced	O
into	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
with	O
the	O
Pentium	O
II	O
Xeon	O
and	O
was	O
initially	O
advertised	O
as	O
part	O
of	O
the	O
"	O
Intel	O
Extended	O
Server	O
Memory	O
Architecture	O
"	O
(	O
sometimes	O
abbreviated	O
ESMA	O
)	O
,	O
a	O
branding	O
which	O
also	O
included	O
the	O
slightly	O
older	O
PAE	O
(	O
and	O
thus	O
the	O
Pentium	B-Device
Pro	I-Device
,	O
which	O
only	O
supported	O
PAE	O
,	O
was	O
advertised	O
as	O
having	O
only	O
"	O
subset	O
support	O
"	O
for	O
ESMA	O
)	O
.	O
</s>
<s>
The	O
heyday	O
of	O
PSE-36	B-General_Concept
was	O
relatively	O
brief	O
.	O
</s>
<s>
PSE-36	B-General_Concept
'	O
s	O
main	O
advantage	O
was	O
that	O
,	O
unlike	O
PAE	O
,	O
it	O
required	O
little	O
rework	O
of	O
the	O
operating	O
system	O
's	O
internals	O
,	O
and	O
thus	O
PSE-36	B-General_Concept
proved	O
a	O
suitable	O
stopgap	O
measure	O
around	O
the	O
Windows	B-Device
NT	I-Device
4.0	I-Device
Enterprise	O
Edition	O
timeframe	O
.	O
</s>
<s>
Newer	O
Microsoft	O
operating	O
systems	O
,	O
including	O
Windows	B-Application
2000	I-Application
,	O
support	O
only	O
PAE	O
.	O
</s>
<s>
Some	O
operating	O
systems	O
like	O
Linux	B-Application
skipped	O
PSE-36	B-General_Concept
entirely	O
.	O
</s>
<s>
Despite	O
this	O
,	O
AMD	O
and	O
later	O
Intel	O
chose	O
to	O
provide	O
up	O
to	O
40	O
bits	O
PSE	O
support	O
in	O
their	O
64-bit	O
processors	O
,	O
when	O
operated	O
in	O
legacy	B-Device
mode	I-Device
.	O
</s>
<s>
Support	O
for	O
PSE-36	B-General_Concept
is	O
indicated	O
by	O
EDX	O
bit	O
17	O
(	O
counting	O
from	O
0	O
)	O
in	O
the	O
cpuid	B-Architecture
result	O
for	O
feature	O
bits	O
.	O
</s>
<s>
As	O
far	O
as	O
activating	O
PSE-36	B-General_Concept
,	O
there	O
is	O
n't	O
however	O
a	O
separate	O
bit	O
from	O
the	O
one	O
that	O
turns	O
on	O
PSE	O
.	O
</s>
<s>
As	O
long	O
the	O
processor	O
(	O
as	O
indicated	O
by	O
cpuid	B-Architecture
)	O
and	O
chipset	O
support	O
PSE-36	B-General_Concept
,	O
enabling	O
PSE	O
alone	O
(	O
by	O
setting	O
bit	O
4	O
,	O
PSE	O
,	O
of	O
the	O
system	O
register	O
CR4	O
)	O
allows	O
the	O
use	O
of	O
large	O
4MB	O
pages	O
(	O
in	O
the	O
64GB	O
range	O
)	O
along	O
with	O
normal	O
4KB	O
pages	O
(	O
which	O
are	O
however	O
restricted	O
to	O
the	O
4GB	O
range	O
)	O
.	O
</s>
<s>
If	O
newer	O
PSE-36	B-General_Concept
capability	O
is	O
available	O
on	O
the	O
CPU	B-Device
,	O
as	O
checked	O
using	O
the	O
CPUID	B-Architecture
instruction	O
,	O
then	O
4	O
more	O
bits	O
,	O
in	O
addition	O
to	O
the	O
10	O
bits	O
used	O
in	O
PSE	O
,	O
are	O
used	O
inside	O
a	O
page	O
directory	O
entry	O
pointing	O
to	O
a	O
large	O
page	O
.	O
</s>
<s>
PDE	O
structures	O
in	O
normal	O
mode	O
,	O
PSE	O
mode	O
,	O
and	O
PSE-36	B-General_Concept
mode	O
are	O
as	O
follows	O
:	O
</s>
<s>
<li>	O
Page	B-General_Concept
attribute	I-General_Concept
table	I-General_Concept
;	O
since	O
Pentium	B-General_Concept
III	I-General_Concept
,	O
must	O
be	O
zero	O
for	O
older	O
CPUs	B-Device
.	O
</s>
<s>
<li>	O
"	O
Dirty	O
"	O
bit	O
:	O
set	O
to	O
1	O
by	O
CPU	B-Device
if	O
there	O
was	O
a	O
write	O
access	O
to	O
that	O
page	O
.	O
</s>
<s>
AMD	O
extends	O
this	O
scheme	O
to	O
40	O
address	O
bits	O
by	O
interpreting	O
bits	O
20	O
..	O
13	O
of	O
a	O
PDE	O
as	O
bit	O
39	O
..	O
32	O
of	O
the	O
page	O
base	O
address	O
in	O
their	O
AMD64	B-Device
processors	O
when	O
operated	O
in	O
legacy	B-Device
mode	I-Device
,	O
so	O
only	O
bit	O
21	O
is	O
reserved	O
(	O
must	O
be	O
zero	O
)	O
.	O
</s>
<s>
Note	O
however	O
that	O
CR4.PSE	O
is	O
ignored	O
in	O
long	B-Application
mode	I-Application
and	O
PSE-style	O
4MB	O
pages	O
are	O
not	O
available	O
in	O
that	O
mode	O
.	O
</s>
<s>
The	O
total	O
amount	O
of	O
physical	O
memory	O
addressable	O
in	O
AMD64	B-Device
legacy	B-Device
mode	I-Device
using	O
PSE	O
4-MB	O
pages	O
is	O
,	O
thus	O
,	O
1024GB	O
.	O
</s>
<s>
The	O
exact	O
number	O
of	O
PSE	O
bits	O
supported	O
on	O
Intel	O
CPUs	B-Device
can	O
be	O
less	O
though	O
,	O
and	O
must	O
be	O
determined	O
by	O
using	O
CPUID	B-Architecture
to	O
query	O
the	O
maximum	O
physical-address	O
width	O
supported	O
by	O
the	O
processor	O
by	O
invoking	O
CPUID	B-Architecture
with	O
function	O
80000008H	O
and	O
checking	O
the	O
result	O
in	O
EAX[7:0]	O
.	O
</s>
<s>
Practical	O
usefulness	O
of	O
the	O
PSE-36	B-General_Concept
feature	O
depends	O
on	O
chipset	O
support	O
for	O
more	O
than	O
4GB	O
of	O
RAM	O
.	O
</s>
<s>
Support	O
for	O
PSE-36	B-General_Concept
(	O
ESMA	O
)	O
was	O
thus	O
usually	O
advertised	O
for	O
servers	O
.	O
</s>
<s>
As	O
suitable	O
operating	O
system	O
supporting	O
PSE-36	B-General_Concept
,	O
in	O
1998	O
Intel	O
advertised	O
Microsoft	B-Device
Windows	I-Device
NT	I-Device
Server	I-Device
,	O
Enterprise	O
Edition	O
4.0	O
and	O
supposedly	O
the	O
upcoming	O
NT	B-Application
5.0	I-Application
,	O
both	O
enabling	O
use	O
via	O
a	O
PSE36	B-General_Concept
device	B-Application
driver	I-Application
,	O
which	O
kept	O
most	O
of	O
the	O
operating	O
system	O
unaware	O
of	O
PSE-36	B-General_Concept
(	O
only	O
the	O
PSE36	B-General_Concept
driver	O
enabled	O
it	O
temporarily	O
)	O
,	O
and	O
which	O
driver	O
had	O
to	O
be	O
called	O
by	O
applications	O
that	O
wanted	O
to	O
access	O
more	O
than	O
4GB	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
4.0	I-Device
Enterprise	O
Edition	O
thus	O
used	O
the	O
PSE-36	B-General_Concept
feature	O
essentially	O
as	O
a	O
RAM	B-Application
disk	I-Application
.	O
</s>
<s>
The	O
PSE36	B-General_Concept
driver	O
was	O
used	O
by	O
some	O
applications	O
on	O
Windows	B-Device
NT	I-Device
4.0	I-Device
Enterprise	O
Edition	O
servers	O
,	O
for	O
example	O
SAP	B-Application
liveCache	O
,	O
Microsoft	B-Application
SQL	I-Application
Server	I-Application
7.0	O
,	O
Oracle	B-General_Concept
8.1.5	O
,	O
and	O
IBM	B-Application
DB2	I-Application
.	O
</s>
<s>
The	O
tuning	O
documentation	O
for	O
the	O
latter	O
noted	O
however	O
that	O
"	O
Unfortunately	O
in	O
most	O
cases	O
performance	O
gains	O
obtained	O
using	O
the	O
PSE-36	B-General_Concept
driver	O
are	O
not	O
spectacular	O
.	O
</s>
<s>
In	O
many	O
cases	O
the	O
server	O
will	O
run	O
slower	O
with	O
8GB	O
using	O
the	O
PSE-36	B-General_Concept
driver	O
than	O
it	O
runs	O
with	O
4GB	O
without	O
the	O
driver	O
.	O
</s>
<s>
 [ ... ] 	O
After	O
more	O
than	O
a	O
year	O
of	O
experimentation	O
and	O
tuning	O
,	O
Microsoft	O
and	O
IBM	O
dropped	O
support	O
for	O
PSE-36	B-General_Concept
due	O
to	O
insufficient	O
performance	O
gains	O
.	O
</s>
<s>
Windows	B-Application
2000	I-Application
(	O
NT	B-Application
5.0	I-Application
)	O
ended	O
up	O
not	O
supporting	O
PSE-36	B-General_Concept
,	O
due	O
to	O
low	O
performance	O
when	O
compared	O
with	O
the	O
alternative	O
PAE	O
.	O
</s>
<s>
Windows	B-Application
2000	I-Application
also	O
replaced	O
the	O
API	O
of	O
the	O
PSE36	B-General_Concept
driver	O
with	O
a	O
new	O
API	O
called	O
Address	B-Device
Windowing	I-Device
Extensions	I-Device
(	O
AWE	B-Device
)	O
,	O
which	O
used	O
PAE	O
underneath	O
.	O
</s>
<s>
(	O
AWE	B-Device
was	O
only	O
available	O
in	O
the	O
Datacenter	O
Server	O
and	O
Advanced	O
Server	O
of	O
Windows	B-Application
2000	I-Application
.	O
)	O
</s>
<s>
starting	O
with	O
Oracle	B-General_Concept
8.1.6	O
or	O
MS	B-Application
SQL	I-Application
Server	I-Application
2000	O
.	O
</s>
<s>
PSE-36	B-General_Concept
was	O
never	O
used	O
by	O
Linux	B-Application
.	O
</s>
<s>
Physical	B-General_Concept
Address	I-General_Concept
Extension	I-General_Concept
(	O
PAE	O
)	O
is	O
an	O
alternative	O
to	O
PSE-36	B-General_Concept
which	O
also	O
allows	O
36-bit	O
addressing	O
.	O
</s>
<s>
PSE-36	B-General_Concept
has	O
the	O
advantages	O
that	O
the	O
hierarchy	O
of	O
page	O
tables	O
is	O
not	O
changed	O
,	O
and	O
that	O
page	O
entries	O
keep	O
their	O
old	O
32-bit	O
format	O
and	O
are	O
not	O
extended	O
to	O
64	O
bits	O
.	O
</s>
<s>
The	O
obvious	O
disadvantage	O
of	O
PSE-36	B-General_Concept
is	O
that	O
only	O
large	O
pages	O
can	O
be	O
located	O
in	O
64GB	O
of	O
physical	O
memory	O
,	O
and	O
small	O
pages	O
can	O
still	O
be	O
located	O
only	O
in	O
the	O
first	O
4GB	O
of	O
physical	O
memory	O
.	O
</s>
<s>
The	O
Intel	O
Extended	O
Server	O
Memory	O
Architecture	O
is	O
defined	O
to	O
include	O
two	O
36-bit	O
addressing	O
modes	O
in	O
the	O
core	O
processor	O
:	O
PAE-36	O
and	O
PSE-36	B-General_Concept
.	O
</s>
